The invention relates to the field of optical components.
One method of increasing the transportable bandwidth in optical communications networks is a technique known as wavelength division multiplexing (WDM). WDM is a technology that combines two or more wavelengths of light for transmission along a single optical waveguide. Each wavelength represents a channel that can carry a bit stream, i.e. content. Wavelength and channel are used herein interchangeably. Transporting two or more wavelengths on a waveguide effectively increases the aggregate bandwidth of the waveguide. For example, if 40 wavelengths, each capable of 10 Gb/s are used on a single fiber, the aggregate bandwidth of the fiber becomes 400 Gb/s.
A similar manner of increasing transportable bandwidth has been termed dense wavelength division multiplexing (DWDM). DWDM generally involves combining a larger number of wavelengths onto a fiber than WDM. While DWDM deals with more difficult issues associated with multiplexing a larger number of wavelengths on a fiber, such as cross-talk and non-linear effects, WDM and DWDM are typically used interchangeably.
A number of optical components are used in WDM networks, such as optical multiplexers (MUX), optical demultiplexers (DEMUX), optical add/drop multiplexers (OADM), wavelength selective switches (WSS) and optical cross connects (OXC). A MUX takes different channels from different waveguides and combines them as a WDM signal into one waveguide. A DEMUX divides a WDM signal received from a waveguide into its different channels and couples each channel into a different waveguide. An OADM selectively removes a subset of the total channels from a WDM signal and selectively adds in the same subset of the total channels with different content. A WSS selectively switches the contents of a subset of the total channels between WDM signals, i.e. amongst L WDM signals that have N channels, the contents of any M of the N channels are selectively switched. An OXC performs the same function as a WSS, except that all N channels are switchable, i.e. amongst L WDM signals that have N channels, the contents of the N channels can be selectively switched.
When one of these optical components can be tuned to operate on different channels by software control, or otherwise, it is generally referred to as being dynamic. If a dynamic optical component can be tuned from operating on a source channel (e.g., channel A) to operating on a destination channel (e.g., channel C) without dropping, switching or otherwise removing intermediate channels (e.g., channel B) from the WDM signal, the component is generally referred to as being hitless. Further, if the bit-error-rate (BER) of intermediate channels is not significantly affected during tuning, then the optical component is generally referred to as being errorless. Lastly, if the optical component contains trimmable elements that allow the component to be fine-tuned for optimal operation, then it is generally referred to as being trimmable.